19.7.7The ADC Data Register – ADCL and ADCH
19.7.7.1ADLAR = 0
Bit |
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
|
|
– |
– |
– |
– |
– |
– |
ADC9 |
ADC8 |
ADCH |
|
|
|
|
|
|
|
|
|
|
|
ADC7 |
ADC6 |
ADC5 |
ADC4 |
ADC3 |
ADC2 |
ADC1 |
ADC0 |
ADCL |
|
|
|
|
|
|
|
|
|
|
|
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
Read/Write |
R |
R |
R |
R |
R |
R |
R |
R |
|
|
R |
R |
R |
R |
R |
R |
R |
R |
|
Initial Value |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
19.7.7.2ADLAR = 1
Bit |
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
|
|
ADC9 |
ADC8 |
ADC7 |
ADC6 |
ADC5 |
ADC4 |
ADC3 |
ADC2 |
ADCH |
|
|
|
|
|
|
|
|
|
|
|
ADC1 |
ADC0 |
– |
– |
– |
– |
– |
– |
ADCL |
|
|
|
|
|
|
|
|
|
|
|
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
Read/Write |
R |
R |
R |
R |
R |
R |
R |
R |
|
|
R |
R |
R |
R |
R |
R |
R |
R |
|
Initial Value |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in ”ADC Conversion Result” on page 135.
19.7.8ADC Control and Status Register B – ADCSRB
Bit |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
|
BIN |
ACME |
IPR |
– |
– |
ADTS2 |
ADTS1 |
ADTS0 |
ADCSRB |
Read/Write |
R/W |
R/W |
R/W |
R |
R |
R/W |
R/W |
R/W |
|
Initial Value |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
• Bits 7– BIN: Bipolar Input Mode
The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided conversions are supported and the voltage on the positive input must always be larger than the voltage on the negative input. Otherwise the result is saturated to the voltage reference. In the bipolar mode two-sided conversions are supported and the result is represented in the two’s complement form. In the unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits + 1 sign bit.
140 ATtiny25/45/85
2586A–AVR–02/05
ATtiny25/45/85
• Bits 5 – IPR: Input Polarity Mode
The Input Polarity mode allows software selectable differential input pairs and full 10 bit ADC resolution, in the unipolar input mode, assuming a pre-determined input polarity. If the input polarity is not known it is actually possible to determine the polarity first by using the bipolar input mode (with 9 bit resolution + 1 sign bit ADC measurement). And once determined, set or clear the polarity reversal bit, as needed, for a succeeding 10 bit unipolar measurement.
• Bits 4..3 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive edge on the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
Table 19-6. |
ADC Auto Trigger Source Selections |
|
||
ADTS2 |
|
ADTS1 |
ADTS0 |
Trigger Source |
|
|
|
|
|
0 |
|
0 |
0 |
Free Running mode |
|
|
|
|
|
0 |
|
0 |
1 |
Analog Comparator |
|
|
|
|
|
0 |
|
1 |
0 |
External Interrupt Request 0 |
|
|
|
|
|
0 |
|
1 |
1 |
Timer/Counter Compare Match A |
|
|
|
|
|
1 |
|
0 |
0 |
Timer/Counter Overflow |
|
|
|
|
|
1 |
|
0 |
1 |
Timer/Counter Compare Match B |
|
|
|
|
|
1 |
|
1 |
0 |
Pin Change Interrupt Request |
|
|
|
|
|
|
|
|
|
|
19.7.9Digital Input Disable Register 0 – DIDR0
Bit |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
|
– |
– |
ADC0D |
ADC2D |
ADC3D |
ADC1D |
AIN1D |
AIN0D |
DIDR0 |
Read/Write |
R/W |
R/W |
R/W |
R/W |
R/W |
R/W |
R/W |
R/W |
|
Initial Value |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
• Bits 5..2 – ADC3D..ADC0D: ADC3..0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC3..0 pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.
141
2586A–AVR–02/05